A Cochrane review [Abstract] 1 included 10 studies with a total of 2 412 subjects. Seven trials analysed different dilutions of vaccines that were produced before smallpox was eradicated and had been stored since then. Three trials compared safety and immunogenicity of new cell-cultured vaccines with the stored, calf lymph-derived vaccine. Four trials included investigations to find out if naive participants differ from non-naive persons in regard to reaction profile and adverse events.
All undiluted vaccines induced a reaction in 95% of people vaccinated in terms of pustule and immunogenicity. Also 1:10 dilutions were fully efficient when the starting concentration was defined. Thus, in case of a bioterrorist attack, at least 1 000 million doses of first generation vaccine would be available, at least to those with access to the stockpile of 100 million undiluted doses. None of the trials investigated the duration of protection. Serious adverse events were reported in 1% to 2% of the volunteers. Fever was observed in 11% to 22% of participants, and headache in roughly half of the participants. Fever was less frequent when new vaccines were administered, but rates of headache were similar in new and old vaccines.
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